TY  - JOUR
A1  - Hannemann, Katrin
A1  - Krüger, Frank
A1  - Dahm, Torsten
T1  - Measuring of clock drift rates and static time offsets of ocean bottom stations by means of ambient noise
JF  - Geophysical journal international
N2  - Marine seismology usually relies on temporary deployments of stand alone seismic ocean bottom stations (OBS), which are initialized and synchronized on ship before deployment and re-synchronized and stopped on ship after recovery several months later. In between, the recorder clocks may drift and float at unknown rates. If the clock drifts are large or not linear and cannot be corrected for, seismological applications will be limited to methods not requiring precise common timing. Therefore, for example, array seismological methods, which need very accurate timing between individual stations, would not be applicable for such deployments.
 We use an OBS test-array of 12 stations and 75 km aperture, deployed for 10 months in the deep sea (4.5-5.5 km) of the mid-eastern Atlantic. The experiment was designed to analyse the potential of broad-band array seismology at the seafloor. After recovery, we identified some stations which either show unusual large clock drifts and/or static time offsets by having a large difference between the internal clock and the GPS-signal (skew).
 We test the approach of ambient noise cross-correlation to synchronize clocks of a deep water OBS array with km-scale interstation distances. We show that small drift rates and static time offsets can be resolved on vertical components with a standard technique. Larger clock drifts (several seconds per day) can only be accurately recovered if time windows of one input trace are shifted according to the expected drift between a station pair before the cross-correlation. We validate that the drifts extracted from the seismometer data are linear to first order. The same is valid for most of the hydrophones. Moreover, we were able to determine the clock drift at a station where no skew could be measured. Furthermore, we find that instable apparent drift rates at some hydrophones, which are uncorrelated to the seismometer drift recorded at the same digitizer, indicate a malfunction of the hydrophone.
KW  - Time-series analysis
KW  - Interferometry
KW  - Broad-band seismometers
Y1  - 2014
U6  - https://doi.org/10.1093/gji/ggt434
SN  - 0956-540X
SN  - 1365-246X
VL  - 196
IS  - 2
SP  - 1034
EP  - 1042
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Pavlova, Viola
A1  - Nabe-Nielsen, Jacob
A1  - Dietz, Rune
A1  - Svenning, Jens-Christian
A1  - Vorkamp, Katrin
A1  - Riget, Frank Farso
A1  - Sonne, Christian
A1  - Letcher, Robert J.
A1  - Grimm, Volker
T1  - Field metabolic rate and PCB adipose tissue deposition efficiency in East Greenland polar bears derived from contaminant monitoring data
JF  - PLoS one
N2  - Climate change will increasingly affect the natural habitat and diet of polar bears (Ursus maritimus). Understanding the energetic needs of polar bears is therefore important. We developed a theoretical method for estimating polar bear food consumption based on using the highly recalcitrant polychlorinated biphenyl (PCB) congener, 2,2',4,4',55-hexaCB (CB153) in bear adipose tissue as an indicator of food intake. By comparing the CB153 tissue concentrations in wild polar bears with estimates from a purposely designed individual-based model, we identified the possible combinations of field metabolic rates (FMR) and CB153 deposition efficiencies in East Greenland polar bears. Our simulations indicate that if 30% of the CB153 consumed by polar bear individuals were deposited into their adipose tissue, the corresponding FMR would be only two times the basal metabolic rate. In contrast, if the modelled CB153 deposition efficiency were 10%, adult polar bears would require six times more energy than that needed to cover basal metabolism. This is considerably higher than what has been assumed for polar bears in previous studies though it is similar to FMRs found in other marine mammals. An implication of this result is that even relatively small reductions in future feeding opportunities could impact the survival of East Greenland polar bears.
Y1  - 2014
U6  - https://doi.org/10.1371/journal.pone.0104037
SN  - 1932-6203
VL  - 9
IS  - 8
PB  - PLoS
CY  - San Fransisco
ER  - 
TY  - JOUR
A1  - Göse, Frank
A1  - Müller, Winfried
A1  - Winkler, Kurt
A1  - Ziesak, Anne-Katrin
T1  - Preußen und Sachsen : Szenen einer Nachbarschaft ; erste Brandenburgische Landesausstellung Schloss Doberlug (7. Juni bis 2. November) 2014
Y1  - 2014
SN  - 978-3-95498-084-0
PB  - Sandstein Verl.
CY  - Dresden
ER  -